As a result of the expanding use of rare earth-bearing materials in modem technology, such as, for example, in the form of rare earth-iron alloy magnetostrictive transducers, delay lines, variable frequency resonators and filters and rare earth-iron-boron alloy permanent magnets, the cost and environmental problems associated with their waste and scrap disposal have become an increasing concern. Additionally, the high cost of rare earth metals makes simple disposal of rare earth-bearing waste or scrap materials economically unattractive. Up to the present time, there have been no large scale operations to recover rare earth metals from scrap and waste materials.
One attempt at recovering rare earth metals from waste and scrap involves dissolution of the waste/scrap material in acid media followed by precipitation of a rare earth compound. The rare earth compound is converted to a rare earth trifluoride which is then reduced to rare earth metal by calcium reduction. U.S. Pat. No. 5,129,945 describes a recovery process of this type. Although the recovery process is effective, it is time consuming and requires the use of expensive non-recoverable reagents.
Another attempt at recovering rare earth metals from rare earth-transition metal materials has produced a process that promises to be less costly and more adaptable to a variety of scrap materials. This process is based on liquid-liquid or liquid-solid extraction technology depending upon the specific rare earth alloy scrap being processed. The process allows rare earth recovery without the expensive and time consuming acid digestion and fluoride reduction steps employed in the recovery process described in the preceding paragraph. Rare earth metals are recovered in this process using reagents which are essentially completely recycled. Thus, the waste stream is kept to a minimum. U.S. Pat. No. 5,238,489 describes a recovery process employing a combination of leaching and flotation to separate different rare earth scrap alloys in a scrap mixture from one another.
U.S. Pat. No. 5,437,709 describes a liquid metal extraction treatment of rare earth-transition metal alloy scrap, waste or other material to rare earth metal components, wherein the process recovers the light rare earth metal and heavy rare earth metal contents of the scrap together. The patent is silent as to how to recover the heavy rare earth metal content separately from the light rare earth metal content of the scrap.
Since Dy is generally considered the most critical, as defined by reserves and costs of the rare earth metals used in RE2Fe14B (where RE =a rare earth metal), development of a process that permits separation of Dy or other heavy rare earth metals from Nd and Pr (light rare earth metals) in their metallic states from permanent magnet scrap is highly desirable to help address potential shortages of Dy. A separation process that yields the heavy rare earth metal content in its metallic form also is preferred over separating processes that separate rare earth metals in their oxide forms, which requires further complicated chemical processing.